If I limit the discussion to just MMOs...
Warhammer Age of Reckoning
Vanguard
Tabula Rasa

All three had major issues with their launch, and had high expectations...tehy were eventually patched/fixed, but too late and lost their audiences.

SW:TOR has been a large disappointment, but the core gameplay and stories are decent; its the lack of endgame that's problematic, and too much of the same as WoW. Their recent F2P conversion is probably going to be a failure though, since it is such a money grab though...

1. Duke Nukem Forever - (WAY over-hyped and defiantly not worth the wait)
2. Daikatana (OMG so bad!)
3. Total Annihilation: Kindoms (HUGE disappointment for me since I was a BIG Total Annihilation fan)

I can't believe I forgot to add Cata. Yeah, HUGE let down, I was so pumped, my first midnight launch ever, first collector's edition, and bam. Awful, awful, awful. Completely turned me away from WoW as a whole. Not to mention the huge drop in subs during Cata.

Interesting considering the massive amount of hype GW2 had pre-release...where had I seen that before...

I can't believe I forgot to add Cata. Yeah, HUGE let down, I was so pumped, my first midnight launch ever, first collector's edition, and bam. Awful, awful, awful. Completely turned me away from WoW as a whole. Not to mention the huge drop in subs during Cata.

Yup. I enjoyed Cata tbh but I don't consider it a success, there were so many game direction changes and difficulty level changes that my toons got whiplash after stepping into a raid.

Hopefully with MoP developers will stick with whatever goal/direction they have for the game.

Wow WOLK: B*tch queen dumbed wow down so hard. it made me quite sad.
Wow Cata: Cakeclisym was borring as hell. had great points but overall was dumb.
SWTOR/Rift/GW2/AoC/"wowkiller": Lol thinking they could kill wow. funny stuff. dont compete with wow. no matter how much they screw it up, they have the established fanbase to float them through.

Till water is gone, Till shade is gone. Into the shadow with teeth bared, screaming defiance with the last breath. To spit in Sightblinders eye on the last day.

I love this game, the only problems it has ever had is due to horrible management. It's like the bosses are completely clueless as to what to push for next and what is the most important. EA was branded the World's Worst Company 2 years in a row for a reason.

While the worst company 2 years in a row may be true, believe it or not they did not have alot to do with SWTOR (outside of being the 'owner' I suppose). That was Bioware's baby; they even outsourced customer service specifically for that game. I called EA raising hell about account problems, and I was politely told "Bioware has full control over that. We are not thrilled about the reports of the poor customer service, trust me, we're ticked off too."

Originally Posted by Standsinfire

Me: whyumad* fixed. Seriously though, it's only because they rapin' eveerbody in here and I don't want you to be snatched out yo' windows.

Originally Posted by noepeen

If that were my dog, I'd Hulk Smash the fuck out of that raccoon.
Or I'd shit my pants.

Practically given a blank check and what do they do with it? Turn it into a WoW clone with lightsabers. A poor, buggy, WoW clone with a lack of endgame content. The stories were good (by no means amazing, this isn't Obsidian we're talking about). With typical BioWare logic they buried their heads in the sand, made a load of false promises and tried to pin blame on the playerbase. When this didn't happen? F2P damage control and lost most of its two million subscribers. Oh, and they probably scared off any big budget MMOs being made for the foreseeable future.

2) Warhammer Online: Age of Reckoning.

See above, typical EA meddling. Dark Age of Camelot and the Warhammer license? What could go wrong?! A lot, apparently. Managed to destroy Myth's reputation in one fell swoop. There's a reason this is regarded as the first big "WoW killer failure". Rushed out to beat WotLK's release date meant that four out of six Capital Cities were removed (this is basically the same as removing four raids from your endgame) as well as four whole classes just to meet that deadline. Like SWTOR it was the biggest MMO launch for its time and the subs fell just as quickly. Good game, terrible execution.

3) Mass Effect 3.

"We want Call of Duties audience" just about sums it up. Buggy, plot holes out of its arse and ears, plus That Ending. No Mass Effect game was without its faults but 3 took the cake, reducing three dialogue options to just two, having Shepard auto-dialogue for half of the game, Day 1 DLC, bugs, bugs and more bugs, just generally shoddy and lazy design work over all (check YouTube), this along with SWTOR and Dragon Age 2 utterly destroyed BioWare's reputation.

Originally Posted by Dekadez

Sandbox MMOs are like having sex with a pornstar: Everyone wants it, but when you're getting it, it's suddenly not so awesome anymore.

Wow WOLK: B*tch queen dumbed wow down so hard. it made me quite sad.
Wow Cata: Cakeclisym was borring as hell. had great points but overall was dumb.
SWTOR/Rift/GW2/AoC/"wowkiller": Lol thinking they could kill wow. funny stuff. dont compete with wow. no matter how much they screw it up, they have the established fanbase to float them through.

I will say on your final point, admittedly none of them said they would compete against WoW (Except maybe RIFT) and most of those still are running as F2P/established games that make a profit, and none of them particularly suck enough to be considered a failure to me. I do get your point though.

Anyway, my list.

Duke Nukem Forever.
Kingdom of Amalur: Reckoning
Revelations 2012
I consider those three the biggest failures, (KoA was more personal to me though.)

You know it was mostly the fanbase claiming they were WoW killers, right? (By fanbase, I mean mostly WoW fanbase tired of the game.) Besides Rift.

And the one that was poking at WoW (Rift) is the only one that seems to be doing just fine. Not sure about GW2 as I haven't followed that. But it seems every single game out there that the playerbase has deemed a "wow killer" has gone free to play/freemium, except for Rift.

SWTOR is really the only one I can come up with. It failed financially and it failed against even the most reasonable expectations of the consumers. I think Global Agenda can sit on that perch as well.

I have a hard time thinking of anything else at the moment...there are games I don't/didn't like that were big commercial successes (most MMS's) and there are games I really like that weren't all that profitable.